The application relates to an optical device for generating images with a three-dimensional effect, having the features described herein.
Optical devices for generating images with a three-dimensional effect rely on the ability of the human brain for three-dimensional vision—that is, the ability of the human brain to fuse information from individual images together, and/or to analyze information fused from individual images in such a manner that a three-dimensional overall effect remains with the viewer.
In other words, such optical devices provide two observation channels with different optical properties, such as different optical paths, different light polarizations, and/or different colors of light, which provide the viewer with information from two different images of the observed object, perceived by the viewer's eyes, which then leads to a three-dimensional perception of the object. It is important in this case that information is fused together. This is done by the brain when the two eyes of a viewer can view the two observation channels at the same time—as is the case with a stereo microscope, for example.
However, the same effect can be achieved particularly with static or nearly static observation objects which do not move or which move slowly, if both observation channels are presented at different times rather than at the same, for example by very quickly switching between two observation channels, or by the fact that images of a first observation channel and images of a second observation channel are captured, for example by using a camera or video camera, and then fused together by—particularly electronic—image processing and observed in the fused state. Accordingly, the three-dimensional effect can be achieved as well for optical instruments which only have one observation channel at a given moment, such as a microscope or endoscope, if the optical properties of the first observation channel are variable—for example by the insertion of variable or interchangeable diaphragms used to influence the beam path, and/or variable or interchangeable filters used for influencing the polarization and/or color of the light. Attention should be directed at this point to the fact, explained in greater detail below, that it is also possible to define the effect of a diaphragm, an aperture or an opening in the beam path with a suitable combination and placement of polarization or color filters, which is why, in the context of this disclosure, the concept of a “diaphragm” also means appropriate combinations of polarization or color filters.
Perhaps the most common type of optical instruments for generating images with a three-dimensional effect are stereomicroscopes.
Stereomicroscopes form a subset of light microscopes, and are distinguished by the fact that they have at least partially different beam paths in the observation channels for the two eyes of a viewer, wherein stereomicroscopes of the Greenough type have one lens per observation channel, and stereomicroscopes of the Abbe type have a shared primary lens for both observation channels. The result of furnishing two observation channels with different beam paths is that the viewer's brain processes two different images, perceived by the viewer's eyes, of the object observed through the stereomicroscope, which leads to a three-dimensional perception of the object.
For this reason, stereomicroscopes are used in many areas in which objects are processed under a three-dimensional view—especially in medicine, where, among other things, they are used as surgical microscopes.
However, one problem of optical instruments for generating images with a three-dimensional effect, in general, and in particular stereomicroscopes, lies in the fact that the desired three-dimensional perception can only be realized if a sufficiently large depth of field is achieved. A small numerical aperture is needed for this purpose, which, in addition to darkening the image obtained, also limits the resolution which can be achieved—but reduces the cost of the microscope.
In contrast, when large numerical apertures are used, it is possible to obtain bright, high-resolution images—with highly complex optics and therefore high costs. However, with these conditions, the achievable depth of field—that is, the area in which an object is in focus—is low, and as a consequence the 3D effects disappear when the object is observed. For this reason, optical instruments for generating images with a three-dimensional effect, in particular stereomicroscopes, having high resolution, are nearly impossible to realize.
As mentioned above, the achievable depth of field can be increased by reducing the numerical aperture. For this reason, stereomicroscopes have already been developed in which the user can adjust the numerical aperture of the observation channels with adjustable diaphragms—for example in the form of iris diaphragms—which, if the adjustment is performed manually, may be forgotten upon a change of user, such that a later user then works under suboptimal conditions.
For this reason, DE 10 2004 006 066 B4, as one example, suggests providing a control unit for aperture diaphragms with adjustable size, said control unit automatically adjusting the size of the opening of the aperture diaphragm as a function of the selected observation parameters—in particular the selected magnification. However, such an automatic adjustment in practice usually does not lead to optimal observation experiences, which is ultimately due to the fact that the best adjustment of the microscope depends on the user's eyes, such that, although a standardized setting may avoid coarse adjustment errors, it also inhibits an individualized modification.
One interesting further approach for furnishing the desired depth of field is described by DE 10 2006 036 300 B4. This document suggests a different design of the two observation channels, in particular with regard to their numerical aperture, and relies on the brain's ability to combine the information from two different observation channels. The stereomicroscope described therein accordingly has one observation channel with a low numerical aperture, higher depth of field, and a dark image, which potentially also has a poorer resolution than the optical magnification would allow nominally, and one observation channel with a high numerical aperture, shallow depth of field, and high resolving power.
However, this solution involves a number of disadvantages. Firstly, cost advantages which are achieved by the substantially identical construction of two observation channels are lost.
Second, if the eyes of the user have different properties, the asymmetric system can lead to a situation in which the eye which is physiologically better-suited to the perception of high-resolution images is assigned to the observation channel with the lower numerical aperture, while the eye which is physiologically less suitable is assigned to the observation channel with a high numerical aperture.
Thirdly, there is a non-negligible risk that the significantly darker image of the channel with the smaller aperture is suppressed when the two images are fused in the mind of the viewer. In general, this phenomenon can be alleviated with a neutral gray filter in the observation channel with a high numerical aperture. However, this then largely cancels out the advantage of the brighter image representation.